This invention relates to flow fields for uniform distribution of fluids or their active components or properties to and from a target area. The flow field may be embodied in a flow field device such as a flow field plate or bipolar plate used for distribution of reactants to, and removal of products from, opposite sides of a catalyzed membrane in an electrochemical cell such as a fuel cell.
A number of references depict flow fields having serpentine channels wherein sequential segments of the channels are parallel, including: U.S. Pat. Nos. 4,686,159; 4,988,583; 5,108,849; 5,252,410; 5,683,828; 5,750,281; 5,773,160; 5,846,668; 5,858,567; 5,858,569; 5,945,232; 6,071,635 and 6,099,984.
A number of references depict flow fields having multiple interleaved serpentine channels wherein sequential segments of each channel are parallel, including: U.S. Pat. Nos. 5,683,828; 5,750,281; 5,773,160; 5,804,326; 5,840,438; 5,858,567; 5,998,055; 6,071,635 and 6,093,502.
A number of references depict interdigitated flow fields, including: U.S. Pat. Nos. 5,252,410; 5,641,586 and 6,207,312. In an interdigitated flow field, channels having an inlet but no outlet alternate with channels having an outlet but no inlet.
In addition, the use of a metal screen as a flow field has been taught, e.g. in U.S. Pat. Nos. 4,855,193; 5,798,187; 6,037,072 and 6,207,310.
U.S. Pat. No. 5,922,485 depicts flow fields having serpentine channels composed of concentric circular segments, as well as straight-line serpentine channels.
U.S. Pat. No. 5,686,199 depicts a series-parallel arrangement composed essentially of parallel segments.
U.S. Pat. No. 6,048,634 depicts flow field patterns wherein pairs of adjacent channels carry flow in opposite directions, including spiral patterns and serpentine patterns wherein sequential segments of the channels are parallel.
U.S. Pat. Nos. 4,631,239 and 4,853,301 describe serpentine flow fields wherein sequential segments of the channels are parallel, where the segments are skewed relative to the boundaries of the bipolar plate and/or relative to the flow field on the opposite face of a bipolar plate.
U.S. Pat. No. 4,292,379 describes flow fields on either side of a bipolar plate wherein the depth and/or separation of parallel channels are varied so as to create an uneven distribution that matches the uneven distribution created by the opposing face of the plate.
U.S. Pat. No. 4,324,844 concerns an electrochemical cell that includes cooling fluid flow passages having varying surface area and spacing.
Briefly, the present invention provides a fluid distribution assembly comprising a flow field device embodying a flow field and a fluid transport layer disposed between the flow field device and a target area, where, for at least one finite non-zero flow rate and at least one use rate of an active component or property of the fluid in the fluid transport layer, lateral flux of the active component or property varies by no more than 35% through at least 90% of all overland portions of said fluid transport layer. In one embodiment, the flow field device comprises a flow field comprising a serpentine channel, comprising non-parallel sequential major segments. In a further embodiment, the angles between successive major segments of the serpentine channel vary progressively.
In another aspect, the present invention provides a flow field device embodying a flow field comprising at least one serpentine channel wherein at least two sequential major segments of the channel are non-parallel.
In another aspect, the present invention provides a flow field device embodying a flow field comprising a channel, where the spacing between analogous parts of sequential major segments of channel decreases monotonically with distance from the inlet, or where land areas separating the major segments decrease in size monotonically with distance from the inlet.
What has not been described in the art, and is provided by the present invention, is a flow field designed to provide uniform lateral flux through the fluid transport layer, and in particular by use of a xe2x80x9czig-zagxe2x80x9d serpentine or xe2x80x9cprogressivexe2x80x9d flow channel.
In this application:
xe2x80x9cflow fieldxe2x80x9d refers to a pattern of one or more channels embodied in a component of a fluid distribution system, which system allows ingress and egress of fluids to and from a target area;
xe2x80x9ctarget areaxe2x80x9d refers to an area having significant extent in at least two dimensions which is served by a fluid distribution system, such as the electrochemically active electrode area of an electrochemical device;
xe2x80x9cactive areaxe2x80x9d refers to the area of a flow field overlaying and serving the target area;
xe2x80x9cactive componentxe2x80x9d refers to a component of a fluid to be used at or in conjunction with the target area, e.g. the oxygen present in air, the hydrogen present in a reformate gas mixture, and the like;
xe2x80x9cactive propertyxe2x80x9d refers to a property of a fluid to be used at or in conjunction with the target area, e.g. the thermal energy content of a coolant, the solvating capacity of a solvent, and the like;
xe2x80x9cserpentinexe2x80x9d refers to a pattern, such as the pattern of a channel in a flow field, comprising sequentially connected major segments which alternate in orientation, such as in orientation of flow direction, and which meet at turning points or are connected by turning segments;
xe2x80x9clandxe2x80x9d or xe2x80x9cland areaxe2x80x9d refer to area between channels or portions of channels of a flow field;
xe2x80x9cmajor segmentxe2x80x9d refers to a segment of a pattern, such as the pattern of a channel in a flow field, having a geometrical orientation distinct from that of major segments directly preceding or following, which is connected to major segments directly preceding or following either at turning points or through relatively short turning segments;
xe2x80x9cfluxxe2x80x9d refers to the transport of a fluid, such as a gas or liquid, which can be expressed in units of kg/s/m2, or the transport of a component of a fluid, e.g. the oxygen present in air, through a given area, which can be expressed in units of kg/s/m2, or the transport of a property of a fluid, e.g. thermal energy which can be expressed in units of watts/m2,
xe2x80x9cflow ratexe2x80x9d refers to the transport of a fluid, such as a gas or liquid, or the transport of a component of a fluid, e.g. the oxygen present in air, and can be expressed in units of mass per unit time (e.g., kg/s) or volume at standard conditions per unit time (e.g., standard cubic centimeters per minute (sccm) or standard liters per minute (slm));
xe2x80x9cfluid transport layerxe2x80x9d means a layer allowing fluid transport, typically a layer of porous or otherwise fluid-permeable structural material, but also including a gap maintained mechanically;
xe2x80x9coverland portionsxe2x80x9d of a fluid transport layer used with a flow field are portions of the fluid transport layer that pass over a land area within the active area of the flow field, which excludes portions of the fluid transport layer that are over a flow field channel or portions not passing over the active area of the flow field;
xe2x80x9clateral fluxxe2x80x9d of fluid through a layer, such as a fluid transport layer, means flux within the layer and generally within the plane of the layer, as distinguished from flux into or out of the layer that may be flux orthogonal to the plane of the layer;
xe2x80x9cflow field devicexe2x80x9d refers to a component of a fluid distribution system which embodies a flow field, typically a component of a fluid distribution system in an electrochemical cell, which is typically either i) a flow field plate or ii) a fluid transport layer that is sufficiently sturdy to hold the pattern of a flow field stamped, molded or cut therein, but which is more typically a flow field plate; which is typically a bipolar plate, which may be made of porous or more typically non-porous material, and which is typically made of electrically conductive material.
It is an advantage of the present invention to provide flow fields and flow field devices capable of highly uniform distribution of fluids or their active components over a target area, which may provide more efficient, stable and durable function in an electrochemical cell.